1. Technical Field
This invention relates to a method for the production of a flash fixing toner and a master batch for use in the method of production. More particularly, this invention relates to the technique for producing a flash fixing toner containing an infrared absorbent.
2. Background Art
For the operation of fixing an image on a material for printing in the electrophotography, the heat roll system has been mainly used heretofore. Since this system contemplates forming an image with a toner on a material for printing such as paper and passing the material carrying the image of toner thereon between opposed heating rolls thereby causing the toner to be deposited fast on the material by thermo-compression bonding, however, it is prone to such problems as exposing a fixing part thereof to the possibility of being clogged, suffering the formed image to be crushed and consequently degrading the resolution thereof, and imposing a limit on the kind of material for printing.
The flash fixing system constitutes itself one version of the non-contact fixing system and proves an excellent fixing system free from the problems encountered by the heat roll system as described above. Since this system requires to fix the toner by the fact that the component in the toner absorbs the light of a xenon flash lamp, particularly the infrared ray, however, it permits only defective fixation of a color toner which profusely uses a coloring material possessing no or only feeble ability to absorb the infrared ray.
As a means for solving the problem of this defective fixation, JP-A-63-161,460 has proposed an idea of causing an infrared absorbent having a light absorption peak at a wavelength in the range of 800-1100 nm to be incorporated by dispersion in the flash fixing toner.
The manufacture of a toner is generally carried out by a continuous procedure which comprises premixing a toner composition comprising a binding resin, a coloring agent, and an electric charge controlling agent in a powder mixing device such as a Henschel mixer, then continuously feeding the resultant mixture to a kneading device such as a biaxial extruding device, melting and kneading the mixture therein thereby inducing dispersion of the additives such as the coloring agent in the binding resin, and pulverizing and classifying the formed blend. The degree with which such additives as the coloring resin are dispersed in the binding resin by the dispersing work and the uniformity of the concentration of the produced dispersion are important factors which affect the solid state properties of the toner.
In the flash fixing toner formed by incorporating therein the aforementioned infrared absorbent, since the degree of dispersion and the inconsistency of uniformity of the infrared absorbent in the toner are factors directly bearing on the fixing of the toner, the degree of dispersion and the uniformity of concentration to be expected of this toner will be very high.
Since the infrared absorbent is incorporated in the toner composition in a small amount as compared with the binding resin, the coloring agent, etc., it is very difficult to render constant the concentration of the infrared absorbent in the toner composition which is continuously melted, kneaded, and extruded during the manufacture of the toner even when the premixing work is carried out thoroughly during the production of the toner.
Further, since the productivity of the toner constitutes itself a very important point, the melting and kneading time to be spent as in the biaxial extruding device during the course of the kneading mentioned above is limited and no longer deserves to be called sufficient for fine dispersion of the infrared absorbent.
The defective dispersion and the ununiform concentration of the infrared absorbent not merely cause inferior fixing of the toner as described above. The infrared absorbent, when suffered to disperse in a localized state, tends to absorb the flash light and emit excess heat and possibly compels the toner part to form voids (white spots in image). In addition to the problem of the ability to absorb the infrared ray, the problem of the charging property to be exhibited to the toner inevitably arises from the structure, the functional group, etc. of the compound of the infrared absorbent.